The present invention relates generally to vehicles powered by internal combustion engines, and more specifically to a control system for operating a vehicle within a limited engine speed range.
It is well known in the art that there is an engine speed at which an engine most efficiently operates based upon one or more criteria. This criteria often includes some weighted combination of fuel economy, reduced emissions and vehicular performance. Engineers are constantly seeking strategies for determining and operating the engine at its xe2x80x9coptimalxe2x80x9d engine speed. One such strategy is engine mapping. Those skilled in the art appreciate that engine mapping is a process of determining the quantity and timing of fuel injections in order to achieve the desired engine speed and satisfy a predetermined criteria. The predetermined criteria are generally aspects of vehicular operation, including but not limited to, fuel economy, vehicular performance, and undesirable emissions reduction.
Typically, the engine map includes the entire range of engine speeds over which the engine is expected to operate. The entire range of engine speeds is based on the vehicle""s duty cycle, or expected range of operation. For instance, for an over the road truck expected to travel within a certain range of speeds and haul a certain range of loads, the entire engine speed range is the range of engine speeds required to power the truck while traveling at any speed and hauling any load within the expected ranges. By mapping the entire engine speed range, the range of engine speeds in which the predetermined criteria is xe2x80x9coptimizedxe2x80x9d can be determined. However, in order to xe2x80x9coptimizexe2x80x9d the predetermined criteria over the entire engine speed range, compromises must be made. For instance, in order to achieve a slight reduction of undesirable emissions at a higher engine speed, the possible reduction of emissions at a lower engine speed, fuel economy and/or vehicular performance may be compromised.
It is also well known in the art that vehicle speed is, at least in part, a function of transmission state and engine speed. Thus, a relatively constant engine speed can be maintained, despite a varying vehicle speed, by adjusting a transmission state or gear. For instance, there are control systems, such as that shown in U.S. Pat. No. 6,260,647 issued to Calamari et al., on Jul. 17, 2001, in which the vehicle speed is controlled independent of the engine speed by adjusting the transmission. Thus, the engine speed can be maintained to power a work machine implement, while the transmission state can be adjusted to control the changing work machine speed. Although the Calamari control system maintains the engine speed by adjusting the transmission state, the Calamari control system is designed to maintain engine speed to power work machine implements, rather than to maximize the efficiency and/or performance of over the road vehicles. The control system is not designed to maintain engine speed at or near the engine""s preferred speed range. Further, although the Calamari control system electronically sets the engine speed, the control system does not electronically determine and set the transmission state.
Lastly, it is also know in that art that, although there are various A combinations of transmission state and engine speed corresponding with a selected vehicle speed and load, there is a combination that corresponds with the selected vehicle speed and load while optimizing fuel economy. Over the years, engineers, based on experience and observation, have realized that a knowledgeable operator can operate the vehicle at the ideal combination of transmission state and engine speed for the selected vehicle speed and fuel economy. In other words, the knowledgeable operator can operate the vehicle while consuming the least amount of fuel for the selected vehicle speed. However, an operator who lacks the appropriate knowledge may operate the identical vehicle at the identical selected vehicle speed as the knowledgeable operator, but use a different combination of transmission state and engine speed. Although both operators are operating the vehicle under identical conditions, i.e., speed and load, the vehicle, when operated by the knowledgeable operator, will consume less fuel than the vehicle, when operated by the unknowledgeable operator.
In one aspect of the present invention, there is a method of operating a vehicle. A limited engine speed range that is less than an entire engine speed range is established, and a vehicle speed is selected. An electronic control module includes a power train algorithm that determines, at least in part, a combination if an engine speed and a transmission state based, at least in part, on the selected vehicle speed and a predetermined criteria. The engine speed is within the limited engine speed range.